Reactor core for thermionic nuclear reactor

ABSTRACT

This invention relates to a reactor core for a nuclear reactor, particularly for a &#39;&#39;&#39;&#39;fast&#39;&#39;&#39;&#39; type nuclear reactor, provided with nuclear fuel, for direct conversion into electrical energy of released heat produced by nuclear fission. The heat-toelectricity conversion takes place by means of thermionic converters having an inner-positioned collector and an outerpositioned emitter. The nuclear fuel is subdivided into subcritical discs whose reactivity is influenced by a change in their mutual distance from each other; and the thermionic converter is imbedded in these individual discs. Additional controls in the form of control rods may also be provided to change the reactivity of the reactor core.

United States [is] 3 683 209 Gross et a1. Aug. 8, 1972 [54] REACTOR COREFOR THERMIONIC 3,176,165 3/1965 Lawrence ..310/4 NUCLEAR REACTOR3,179,822 4/1965 Block ..310/4 [72] Inventors: Franz Gross,Neckargemund; Ru-

E -T et do" Krapf Leimen both of Gap c ut many 3,439,193 4/1969Bensussan ..310/4 3,440,455 4/1969 Stahl et a1 ..176/39 [73] Assignee:Brown, Boveri & Cie A.G., Mannheim-Kafertal, Germany PrimaryExaminerReuben Epstein Filed Dec 29 1967 Attorney-Nathan M. Briskin [21]App1.No.: 694,592 [57] ABSTRACT This invention relates to a reactor corefor a nuclear [30] Foreign Application Priority Data reactor,particularly for a fast type nuclear reactor, provided with nuclearfuel, for direct conversion into 1967 Germany 90576 electrical energy ofreleased heat produced by nuclear [52] U S Cl 310/4 176/39 fission. Theheat-to-electricity conversion takes place [51] ln.t.cl H62 3/00 y meansof thermionic converters having an inner [58] Field i 310/4 positionedcollector and an outer-positioned emitter. The nuclear fuel issubdivided into sub-critical discs whose reactivity is influenced by achange in their mu- [56] References Cited tual distance from each other;and the thermionic con- UNITED STATES PATENTS verter is imbedded inthese individual discs. Additional controls in the form of control rodsmay also be jablonsktl l provided to change the reactivity of thereactor core. anner e a 3,079,320 2/1963 Weill ..176/21 5 Claims, 3Drawing Figures REACTOR CORE FOR THERMIONIC NUCLEAR REACTOR BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates toimprovements in nuclear reactors provided with thermionic converterdevices for direct conversion of the released heat into electricalenergy. For background information, reference is made to the copendingapplication entitled Nuclear Rector With Thermionic Converters, Ser. No.637,822, May 1 l, 1967, of Kurt Stahl, Reinhart Langpape, and Ned S.Rasnor now US. Pat. No. 3,440,455, dated Apr. 22, 1969, and also thecopending application entitled Thermionic Fuel Rod With Nuclear fuel,Ser. No. 657,820, Aug. 2, 1967, of Franz Gross et al.; and particularlyour earlier filed copending application Ser. No. 670,187, Sept. 25,1967, all assigned to the assignee of the present application. Forfurther background literature, reference may be had to the articleentitled Entwurfsstudie einer Energieversorgungsanlage furRaumfluggerate mit einem thermischen Kernreaktor (TRlKT-SO) (translatedas Outline of a Power Supply Installation for Space Vehicles with aThermionic Nuclear Reactor (TRIKT -50)) by Von W. Haug et al.,Atomkemenergie, th yr. (1965), Vol. 9/ 10, pp. 363-367.

2. Description of the Prior Art Thermionic energy transducers orconverters are used for converting heat energy directly into electricalenergy. The converters are comprised of two closely spaced adjacentelectrodes, one of which, known as the emitter, is so strongly heatedthat it emits electrons, which are then removed by the other electrode,known as the collector. The resulting difference of the respectiveoutlet terminals is available as a source of electrical energy.

As is known from thermionic emission tubes, a negative space chargeoccurs in front of an electronemitting surface, which impedes thefurther output of electrons. For this reason, the distance or interspacebetween the electrodes is made quite small, or the negative space chargeis compensated by positive ions. For this purpose, caesium vapor isprimarily supplied to the interspace between the electrodes.

Known nuclear fission processes may be used as a heating source. Inknown devices for thermic reactors, the nuclear fuel is assembled withthe electrodes into a thermionic converter, several of which beingelectrically connected in series as a thermionic fuel rod. In theseknown present devices, the nuclear fuel is disposed inside of theemitter. The resulting fission gases are collected in a special space orchamber from which they are continuously pumped off.

Such nuclear fuel rods as above described form, for example, togetherwith the moderator, the reflector, and the regulating or control rods, athermic nuclear reactor. For further background information and detailsreference may be had to the above-mentioned article in the periodicalpublication: Atornkem-Energie, 1965, volume 9/10, page 365 et seq. Whensuch nuclear reactors as therein described are intended to be sued inspace vehicles to supply energy for the airborne equipment, the goalshould be the least possible capacity weight (i.e. mass per capacityunit), since the mass plays such a decisive role in such uses due to thehigh cost of transport.

For this reason, fast reactors are preferred for large capacities over200 kW,. since the absence of the moderator in the reactors permits amore compact device at a lower capacity weight. Thus, it has beensuggested, for example, in a known embodiment described in theabove-mentioned article in the periodical publication inAtomkem-Energie, 1965, volume 9/ 10, at page 368, to install thethermionic fuel rods in the fission zone region of a fast reactor, inthe form of a hexagonal grid or control electrode within the pressurecontainer.

Fast reactors which are designed for a capacity range up to 2 MW,,, (twoMegawatts of thermal power output) must contain about 50 percent oftheir total weight in nuclear fuel, so that the entire device couldstill become critical. Approximately 35 percent of the nuclear corevolume must furthermore be used for coolants, so that only about 15percent of the volume portion of the core remains available for thethermionic fuel rods or elements.

This kind of distribution of the volume for the nuclear fuel and theknown types of thermionic fuel rods or elements cannot be attained,within the abovediscussed output capacity range, in a device whichcontains the nuclear fuel inside a cylindrical emitter.

To avoid these above-described short-comings of the prior art, ourearlier filed patent application Ser. No. 670,187., filed Sept. 25,1967, described thermionic converters or transducers comprisingconcentric collectors and emitters, the collectors being disposed asinside electrodes and the respective emitters being disposed as outsideelectrodes, surrounded by the nuclear fuel. In this instance, the insidechamber of the collector contains the equipment for the inlet and outletof the coolant. The equipment may be designed as concentric pipes,arranged for flow in the counter-current directions, or asthrough-pipes. As a further improvement, if the thermionic convertersare electrically connected in parallel, the cooling cycle equipment mayserve, at the same time, as a conductor for the collector currents.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide the most favorable device to serve this latterpurpose. The present invention is characterized by the fact, first, thatthe nuclear fuel is sub-divided into subcritical discs whose reactivityis influenced by providing means for changing their mutual distancesbetween each other, and secondly, through the fact that the convertersare imbedded inside the individual fuel discs. It is a known fact thatthe reactivity of a nuclear reactor is a measure of the rate ofproduction of neutrons, that is, the resultant flow of neutrons.

According to a further embodiment of the invention, the reactivity ofthe core is changed by additional adjustable control rods arranged in amanner known per se. Such adjustable control rods may be the only meansfor changing the reactivity of the core, the discs then being fixed withrespect to each other, or the control rods may be employed in cores inaccordance with the invention wherein the discs are adjustable towardand away from each other.

Brief Description of the Drawing The above and further objects and novelfeatures of the invention will more fully appear from the followingdescription when the same is read in connection with the accompanyingdrawings. It is to be expressly understood, however, that the drawingsare for the purpose of illustration only, and are not intended as adefinition of the limits of the invention.

In the drawings, wherein like reference characters refer to like partsthroughout the several views,

FIG. 1 is a view in cross section through the reactor, the section beingtaken parallel to the axis of the reactor;

FIG. 2 is an enlarged view of a detail of FIG. 1; and

FIG. 3 is a series of top plan views looking down upon a disc, therespective quadrants I, II, III, and IV thereof illustrating respectiveinterconnected portions of the discs.

Description of the Preferred Embodiments As illustrated in FIG. 1, thesub-critical mass of nuclear fuel 1 is disposed in a cylindricalmetallic enclosure 2. The metallic enclosure and the nuclear fuel form adisc; four such discs are shown in FIG. 1, such discs being designated13a-13d. Such enclosure 2 comprises a so-called cladding and issurrounded by a heat insulating wall 7. Centrally located along the axisof the device is a duct or channel which receives the leads or lineswhich all of the thermionic converters of the unit have in common. Suchleads include 11a, 11b for the supply of caesium vapor, 12a, 12b for theinlet of coolant, 16a, 16b for the outlet of coolant, and 14a, 14b forthe current-carrying leads.

The cladding 2 also serves for holding and supporting the emitter 3 ofthe individual thermionic converters or transducers. The cladding 2 hasupper and lower walls and peripheral inner and outer walls which providea chamber for receiving nuclear fuel. The converters are distributed atleast substantially uniformly over the area of the disc formed by thecladding 2, the emitters 3 of the converters being surrounded by thenuclear fuel. Each of the converters comprises an emitter 3, made in theform of a cylindrical tube, and a collector 4 (FIG. 2) positioned withinthe emitter at least generally coaxial thereof. The emitter andcollector are separated from each other by insulation rings 5, as morefully described in our above-mentioned copending application Ser. No.657,820, such insulating rings forming an electrode space which isfilled with caesium vapor. At the same time, the collector forms theouter jacket or housing of the tubes 6 through which the coolant,flowing in a cycle, passes. The caesium vapor is supplied to allconverters, via a network of pipelines 11a, 11b and the respective duct9, in the collector or emitter, into the intermediary space between theelectrodes. The leads or connecting lines 16a, 16b serve for supplyingthe coolant to the tubes 6, whereas the leads 12a, 12b serve to supplycoolant to tubes 6. The current collectors 8, 10 of the converter may beelectrically connected in series as shown in Segment HI in FIG. 3 or inparallel as shown in Segment IV, depending upon the current-voltagerequirements.

The aforedescribed combination of cladding, nuclear fuel, and otherparts of the composite converter is positioned axially centrally withina reflector housing 18 by means of guides which permit their adjustmentaxially of the housing 18, and are adjusted by means of mechanicaldevices (not shown) well known in the reactor art. In accordance withthe present invention, a plurality of these composite converters, spacedaxially from each other as shown in FIG. 1, form the core of a fastreactor.

FIG. 3 shows a topview looking down upon a converter device, in such away that each quadrant shows only a portion of the connections of theindividual converters, namely:

Quadrant I, the caesium supply;

Quadrant II, the inlet and outlet of the coolant;

Quadrant 111, an electrical series-connection of the converters; and

Quadrant IV, an electrical parallel-connection of the converters.

It will thus be seen that the connected structures of Quadrants I, II,and HI of FIG. 3 show one converter in accordance with the invention,and that the connected structures of Quadrants I, II, and IV of FIG. 3show another converter in accordance with the invention.

The output control or regulation of this reactor may be effected, forexample, by varying the distances of the individual converter devicesfrom each other; such variation changes the reactivity of the reactor.The discs 13a-I3d are selectively moved closer to an further away fromeach other by conventional means as shown. A change in reactivity mayalso be effected by a rough control produced by the change in distancebetween individual converters, while precise regulation or control iseffected, in a known manner, by means of additional control rods, suchcontrol rods being selectively inserted into the reactor to control therate of production of neutrons therein.

Finally, the individual converter devices may be attached within thereflector at fixed distances from each other, and the requiredreactivity changes may be effected only by means of control rods.

In accordance with the present invention, the resulting specific weightof the reactor core is low. An additional advantage lies in the factthat the radioactive gases, released during nuclear fission, diffusefrom the nuclear fuel through pores or openings provided in the cladding2, into a mutual fission gas chamber so that the fission-gasventilation, which is provided in each conventional converter or fuelrod, is eliminated.

Although a limited number of embodiments of the invention have beenillustrated in the accompanying drawings and described in the foregoingspecification it is to be especially understood that various changes,such as in the relative dimensions of the parts, materials used, and thelike, as well as the suggested manner of use of the apparatus of theinvention, may be made therein without departing from the spirit andscope of the invention, as will now be apparent to those skilled in theart. Thus in accordance with the present invention several of the abovedescribed converters may be combined into short fuel rods which areemployed in the devices shown in FIG. 1.

We claim:

1. A themiionic device for converting heat directly into electricalenergy, comprising, in combination a plurality of superposed aligneddiscs forming a fast reactor core and each having a space defined by acylindrical enclosure to receive nuclear fuel of subcritical dimension,nuclear fuel in said enclosure, thermionic converters affixed to each ofsaid discs within the borders thereof, each of said converters having acollector and an emitter with the emitter outwardly disposed withrespect to the collector, the collectors and emitters being spaced fromeach other, and insulating ring means forming a sealed electrode spacedisposed between respective collectors and the emitters, the emittersbeing in contact with the nuclear fuel disposed in said space.

2. A device according to claim 1, wherein said emitter is in the form ofa cylindrical tube and is positioned externally of said collector.

3. A device according to claim 1, wherein said discs are hollow and haveupper and lower walls, and the nuclear fuel receiving space in each saiddisc is bounded by said upper and lower walls.

4. A device according to claim 1, wherein the discs are enclosed withina reflector housing and form a fast reactor core, said housing having atop opening for inlet and outlet leads.

5. A device according to claim 4, wherein the aligned discs arevertically spaced within the housing.

1. A thermionic device for converting heat directly into electrical energy, comprising, in combination a plurality of superposed aligned discs forming a fast reactor core and each having a space defined by a cylindrical enclosure to receive nuclear fuel of sub-critical dimension, nuclear fuel in said enclosure, thermionic converters affixed to each of said discs within the borders thereof, each of said converters having a collector and an emitter with the emitter outwardly disposed with respect to the collector, the collectors and emitters being spaced from each other, and insulating ring means forming a sealed electrode space disposed between respective collectors and the emitters, the emitters being in contact with the nuclear fuel disposed in said space.
 2. A device according to claim 1, wherein said emitter is in the form of a cylindrical tube and is positioned externally of said collector.
 3. A device according to claim 1, wherein said discs are hollow and have upper and lower walls, and the nuclear fuel receiving space in each said disc is bounded by said upper and lower walls.
 4. A device according to claim 1, wherein the discs are enclosed within a reflector housing and form a fast reactor core, sAid housing having a top opening for inlet and outlet leads.
 5. A device according to claim 4, wherein the aligned discs are vertically spaced within the housing. 